Our previous results revealed a high degree of variation of IGF1R levels in cancers (Cao et al., Cancer Res. 68: 8039-48, 2008) showed a direct correlation between the levels of IGF1R in cancer cells and the anti-proliferative response to anti-IGF1R antibodies. Cancer cells expressing elevated IGF1R ( greater than 30,000 copies per cells) were very sensitive to IGF1R antibody. Our data suggested that tumor cells had a high degree of dependence on elevated IGF1R for maintaining high AKT signaling, both in vitro and in vivo. The inhibition of IGF1R with therapeutic antibodies resulted in a dramatic reduction of AKT signaling in tumor cells with elevated IGF1R. In our current study, we identified a model system in which IGF1R antibody selectively induced rapid tumor cell death in vitro and in vivo. Our results illustrate the mechanism of anti-IGF1R-induced cancer cell death mediated via AKT and BclxL. Tumor cells without elevated Bcl2 had a greater degree of dependence on IGF1R and AKT signaling, and thus, more susceptible to anti-IGF1R induced cell death. Our data further showed a dual function for IGF1R in tumor growth and survival. This work results in a paper in press for oncogene (Mayeenuddin et al., Oncogene. 2010. In Press.)